Absorbent paper



Patented May 6, 1 930 UNITED STATES PATENT OFFICE Gnome scnwAn'rz, or w'mmme'ron, EL WARE, ASSIGNOR 'ro I. no PON'E :on

unmouns a COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION or :oELA- Io Drawing. Application filed November 10 such as, for examflplgroofing paper, artificial leather and the l v It is known that by various treatments, cellulose fibre, for example, wood pulp, maybe made up into a paper having various degrees of porosity, water absorption, etc. .However, the degree of porosity attainable in prior art practice has been limited, and, in general, the strength of such products, both in the wet and in the dry state, has been low.

One object of the present invention is an improved process of producing a porous mat,

. of cellulose fibre. Anotherobject is to convert a cellulose fibre mat or paper into. a feltlike substance useful for various purposes'in' the arts requiring strength, high porosity, high absorption for water and'other liquids, and lowheat -conductivityr Still another object is to produce a strong, porouspa er.

I have discovered that a cellulose ref mat or paper havin high degree of porosity and low apparent ensity, as well as other desirable properties, may be prepared by treating 'a sheet of cellulose fibre mat, for example, kraft paper, with a gelatinizing reagent under definite conditions of temperature and concentration until the required degree of gelatinization is" attained, and thereafter washing out the gelatinizing reagent. During the gelatinizatioii of the cellulose, Water is taken up and the individual fibres swell to many times their original diameter. As a result, the sheet contracts somewhat in area and expands to several times its original reagent, the individual fibres shrink to "a point only slightly greater than the original diameter, but the thickness of the gelatinized sheet is retained." The result is a highly por- 0fis,. felted, sheet resembling chamois in texthickness. ()n washing'out the .gelatinizing ture and having unusual strength, both in the AasoRBEN'r PAPER 9, 1927. Serial no. 232,192. 1

wet and in the dry state. This product is pliable and retains its strength to a large ex-' tent even in the wet state. Because of its porosity and the peculiar conformation of tremely low conductivity for heat.

As the raw material in my process, I may use a mat of cellulose fibre in sheet form, for example, kraft, jute or sulfite paper. I preis notreadily soluble in the gelatinizin'greagent under the conditions of use. Iprefer' also, in most cases, to use as a starting material paper containing little or no sizing, filler or otherTmaterial capable of retarding the wetting ofthe fibres by the gelatinizing reagent.

ous solution of caustic soda, caustic potash or other fixed caustic alkali at a cencentration between 2 and 11 mols caustic per hundred mols water. For many purposes I prefer to maintain the alkali concentration between 2.5 and 8 mols caustic per hundredmols water. I gelatinize the cellulose fibre the required degree by treatingwith the gelatiniz- As the gelatinizing reagent, I useoan aquee5- fer to use paper having cellulose fibre which ing reagent at \a' temperature between the Y [freezing point of the reagent and a point about 20 C. higher. Iimmerse the fibre in the 'gelatinizi ng reagent at the specified temperature. until the desired degree of gelatinizat'ion'is accomplished. This reaction takes place very quickly, and'as a rule the treatment need not'be continued for more than 15 or 20 seconds. However, this will depend somewhat .on t%e the sheet, the nail product to be prepared, and the presence or absence in the fibre of ,materials; for example, size, filler, etc., which affect the rate of wetting of the fibre by the l'gelatinizing reagent. By theterm superficial gelatinization as used in the claims and effected in the short timementioned above, I mean a gelatinization which does not go fibre used, the thickness of 60 its fibrous structure, this product has-an ex-- substantially beyond thesurface of the fibres and which does not penetrate to the interior of the fibre so as to destroy the fibre identity or to cause the production of other than the porous product described. No claims are made herein to the process of treating paperchanges in alkali concentration due to freezing. The most favorable temperatures for carrying out the process of the invention are 1 contained within a range between the freez ing oint of the-reagent and a point about 20 hi her.' In general, the solubility of cellulose bres in dilute-caustic solutions increaSeswith decreasing temperatures, and

with some grades. of fibre becomes marked at temperaturesnear the freezing point of the solution. When using such grades of fibre it" is' preferable to o erate at a somewhat higher temperature t an otherwise. When usingades of fibre which are soluble in the ge atinizing reagent at the freezing point, it is preferableto carry out the gelatinizing reaction of a temperature which is between the up er temperature limit at which the fibre is rea ily soluble in the reagent and a point about 20 C. higher. v

The exact procedure followed in the proc ess of the invention may be varied within wide limits. For exam lo, I may bring the gelatinizingreagent to t e required temperature and merely dip therein the paper or sheet to be treated, until the elatinizmg re action has proceeded to the esired degree; then remove thesheet from the reagent and wash withwater to remove the. gelatinizing reagent. According to another-modified procedure, I'may firstdip the mat or paper to be treated into a caustic solution at a temperature above the gelatinizing range, then remove to a bath of the reagent at the gelatinizing temperature, and follow by washing and drying. In this case, the time required for treatment in the gelatinizing bath is reduced, since the fibre is already impregnated with the caustic solutiom. In still another modification of my procedure, I may treat the paper in a continuous sheet, using a continuous process by which the paper is carried on a belt through a connected series of baths in which the'sheet to be treated is first immersed in caustic alkali of specified concentration, then in order through a gelatbath maintained'ht the specified, temperature, through a series of washings, and finally through a drier. If desired, the last traces of alkali may, be neutralized by acid,

\ followed by washing and drying. When using the continuous process as described above,

it is possible to reduce the alkali requirements of the process to a minimum.

- Another form of my process, useful in some cases, is to impregdate the paper with the alkali reagent at a temperature above the gelatinizing range, then bring about a reduction in temperature to the gelatinizing point by placing the impregnated paper between metal sheets maintained at the required temperature. When the cellulose is sulficiently gelatinized, it is removed from the 'metalsheets, washed and dried.

In another modification, I may impregnate the paper with the gelatinizing reagent at a temperature above the gelatinizing ran e, then lower the temperature to the gelatinizing point to bring about the gelatinization of the fibre, thenraise the temperature above the gelatinizingrange to stop the reaction,

I have also found that if pressure is applied to the cellulose fibre after the gelatinization step and while the fibre is still in the gelatinized condition, at least a portion of the fibres are welded together-,which results in a marked increasein strength in the finished product' and otherwise improves it. This pressure may be applied by the useo'f squeeze rolls, wire screening, or metal plates which may or may not be perforatedafter-treatment of the gelatinized fibre for the purpose of depositing salt crystals within the pores of the fibre uring drying and In still another form of myprocess which is useful for many purposes, I modify tha thereby increasingthe pufling action on the 1 sheet. For example: I remove the sheet from the gelatinizing bath and without washing I festoon the sheet in contact with air and allow to dry. The carbon dioxide in the air combines withthe caustic in the solution which wetsthe sheet forming Na CO As the sheet dries, the carbonate crystallizes out'as M1 00 1Q H50 and the formation of these crystals within the pores of the sheet greatly increases the pullin action and decreases the apparent density OI thesheet. Instead'of air I may use carbon dioxide, stack gas or other atmosphere containing carbon dioxide or other acid as capableof combining the caustic soda to orm a water soluble crystallizable salt. To 1 increase the volume of the salt crystals in this after-treatment, I may follow the gelatinizing bath with an after-bath in which I use a caustic sodasolution of higher concentration than the" gelatinizing reagent. I thus obtain an increased volume of salt crystals and cor responding increase in the pulling effect. Instead of caustic soda-in the after-bath, I may use a solution ofa crystallizable salt, such, for example as, sodium carbonate, sodium sulfate, and the like, or I may use an acid salt, such, for example, as sodium bicarbonate, in such proportions that'when combined with the caustic already present, a normal crystallizable salt is formed; for example, normal sodium carbonate. the, sodium carbonate or other crystallized salt is removed from the sheet by washing and there remains a tough pliable sheet having high porosity and high specific volume.

I have also found in producing a porous or puffed paper product by treating with caustic soda and drying in air, that clearly improved and strictly uniform results may be obtained if the air or other carbon dioxide containing gas, which is used in drying, is

carefully conditioned before entering the drier or before bringing into contact with the wet paper. To produce any given product in uniform quality, the air or other gas is conditioned so that temperture and humdity are substantially constant. Excellent products may thus be obtained by conditioning the air to a substantially constant humidity at a point above humidity and to a substantially constant temperature at a point below 34 C. To obtain maximum putfing effect, the air entering the drier is conditioned to a humidity which is substantially constant at a point above 20% and at a temperature which is substantially constant at a point below 15 C. The humidity may be controlled at a given point by known methods as, for exam ple, by passing the air through a salt solution having the required vapor pressure.

In comparison with prior art processes of.

producing porous cellulose fibre products, the process of the present invention has the advantage that it is more expeditious and is more economical. By the process which I have described, I am able to produce various forms of porous paper and the like which have a highabsorption for water and other liquids. These products have high specific volume, low heat conductivity and are not readily separated into laminations by mechanical treatment. When used as paper toweling, my product is practically'free from linting whichis a common defect of paper toweling products as made by previously known processes. y As many apparently widely different variations of this invention may be made with-.

out departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing examples or description except as indicated in the following patent claims.

I claim:

1. A process for producing aporu's felted cellulose fibre product which comprises treating a cellulose fibre matin the form of a sheet.

with a gelatinizing reagent comprising fixed caustic alkali and water in the'proportion of 2 to 11 mols caustic perhundred mols water, at a temperaturev between the freezing point After the sheet is driedof the gelatinizing reagent and a temperature about 20 C. above'said freezing point, until the cellulose fibre is superficially gelatinized,

then removing the sheet from the gelatinizing reagent and washing the sheet to substantially free it from said reagent. F

, 2. A process for producing a porous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet and containing cellulose fibre which is not more than slightly soluble in the gelatinizing reagent under the conditions of working, with "a gelatinizing reagent containing fixed caustic alkali and water in the proportion of from .2 to 11 mols caustic per hundred molswater,

at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized, then removing the sheet from the gelatinizing reagent and washing substantially free from said reagent.

3. A process for producing a porous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the proportion of 2.5 to 8 mols caustic per hundred mols Water, at a temperature between the freezingpoint of-the gelatinizing reagent and a temperature about 20C. above said freez ing point, until the cellulose fibre is superficially gelatinized, then removing the sheet from the gelatinizing bath and washing the.

perature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized, then removing the sheet from the gelatinizing bath, and washing substantially free from said reagent.

5. The process set forth in claim 1 in which the mat is first dipped into a caustic solution at a temperature above the gelatinizing range and the temperature then reduced to the gelatinizing point.

6. The process set forth in claim 1 in which the mat is first impregnated with the gelatinization reagent at a temperature above the gelatinizing range,thetemperaturethen lowered to the gelatinizing point to bring about the gelatinization of the fibre", then the temperature raised'above the gelatinizing range to stop the reaction. i.

7. A process for producinga porous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the proportion of within the sheet.

8. A process for producing a porous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet and containing cellulose fibre which is not more than slightly solublein the gelatinizing reagent under the conditions of working, with a gelatinizing reagent containing fixed caus tic alkali and Water in the proportion of from 2.5 to 8 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized, then removing the sheet from the gelatinizing bath, drying the sheet in contact with a gas capable of combining with the caustic alkali to form a water soluble crystallizable salt,

9. A process for producing a porous felted cellulose fibre product which comprises treat-,

ing a cellulose fibre mat in the form-of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the proportion of 2 to 11 mols caustic per hundred mols water,

at a temperature between the freezing. point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized,

then removing the sheet from the gelatinizing bath, drying the sheet in contact with a gas containing carbon dioxide, washing and drying the sheet.

10. A process for producing aporous felted cellulose fibre product which comprises treat L ing a cellulose fibre mat in the form of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the proportion of 2 to 11 mols caustic per hundred mols water,

at a temperature between the freezing point of the gelatinizing reagent and a temperature reagent under the conditions of working, with a gelatinizing reagent containing fixed caustic alkali and water in the proportion of from 2 to 11 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized, applying pressure to the gelatinized fibre, then removing the sheet from the gelatinizin reagent and washing substantially free rom soluble salts.

. 12. A process for producing a porous felted I cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet and containing cellulose fibre which is not more than slightly soluble in the gelatinizing reagent under the conditions of working,

with a reagent containing fixed caustic alkali and (water in the proportion 'of from 2 to 11 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and (a teinperature about 20 C. above said freezing point, drying the fibre by contacting with a carbon-dioxide-containing gas of initially substantially constant temperature below 34 C. and humidity above 50%, and washing: the cellulose fibre to substantially free ,it from the soluble salts.

13. A process for producing a porous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the propors .tion of 2 to 11 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, until the cellulose fibre is superficially gelatinized, applying pressure to the gelatinized fibre, drying the fibre bycontacting with a carbon-dioxide-containing gas of initially substantially constant temperature below 34 C. and "humidity above 50%, and washing the cellulose fibre substantially-free from'the soluble salts.

14; A process for producing a porous felted ing a cellulose fibre mat in the-form of a .sheet and containing cellulose fibre which is not more than slightly soluble in the gelatinizing reagent under the conditions of working, with a reagent containing fixed caustic alkali and water in the proportion of from 2 to 11 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 C. above said freezing point, drying the fibre by contacting with a carbon-dioxide-containing gas of initially substantially constant temperature below 15 C. and humidity above 20%, and washing the cellulose fibre substantially free from the soluble salts. A

cellulose fibre product which comprises treat- 15. A process for producing aporous felted cellulose fibre product which comprises treating a cellulose fibre mat in the form of a sheet with a gelatinizing reagent comprising fixed caustic alkali and water in the proportion of 2 to 11 mols caustic per hundred mols water, at a temperature between the freezing point of the gelatinizing reagent and a temperature about 20 0. above said freezing point, until the cellulose fibre is superficially gelatinized, applying pressure to the gelatinized fibre, drying the fibre by contacting with a carbon-dioxide-containing gas of initially substantially constant temperature below 15 C. and humidity above 20%, and

washing thecellulose fibre substantially free from'the soluble salts.

In testimony whereof, I aifix my signature.

GEORGE L. SCHWARTZ. 

